Vapor compression refrigeration cycle devices including at least the following as constituent elements are conventionally known: a compressor that compresses and discharges refrigerant; a radiator that radiates heat from refrigerant discharged from the compressor; a pressure reducing device that reduces the pressure of refrigerant flowing out of the radiator; and an evaporator that evaporates refrigerant depressurized at the pressure reducing device. Refrigeration cycle devices with various types of cycle configuration have been proposed as this type of refrigeration cycle device to enhance cycle efficiency (COP).
For example, Patent Document 1 (JP 2001-235245A) discloses regarding a so-called economizer refrigeration cycle device. The economizer refrigeration cycle device is provided with two compression mechanisms, a lower stage compression mechanism and a higher stage compression mechanism, as a compressor to compress refrigerant in multiple stages. In this type of economizer refrigeration cycle device, the intermediate-pressure refrigerant of the cycle is joined with refrigerant discharged from the lower stage compression mechanism and the merged refrigerant is drawn into the higher stage compression mechanism.
As a result, the pressure difference between drawn refrigerant pressure and discharged refrigerant pressure, in both the lower stage compression mechanism and the higher stage compression mechanism, is reduced. The compression efficiencies of both the compression mechanisms are thereby enhanced to enhance the cycle efficiency.
Patent Document 2 (2008-107054A) discloses a so-called ejector refrigeration cycle device adopting an ejector that functions as a refrigerant circulating portion. In this type of ejector refrigeration cycle device, refrigerant is isentropically depressurized at a nozzle portion for driving of the ejector to convert pressure energy into kinetic energy.
Refrigerant flowing out of an evaporator is drawn by the suction action of high-speed sprayed refrigerant sprayed from the nozzle portion. Then the velocity energy of the sprayed refrigerant is converted into the pressure energy of drawn refrigerant at the diffuser portion of the ejector. The pressure of compressor drawn refrigerant is thereby increased to reduce the driving power of the compressor and enhance cycle efficiency.
Patent Document 3 (JP 2010-133606A) proposes an economizer refrigeration cycle device (two-stage pressure-increasing ejector refrigeration cycle device) provided with an ejector. With the economizer refrigeration cycle device, it is possible to obtain both the cycle efficiency enhancement effect from the economizer refrigeration cycle device and the cycle efficiency enhancement effect from the ejector refrigeration cycle device.
The cycle efficiency (COP) is defined as the ratio (ΔH/L) obtained by dividing the refrigeration capacity ΔH delivered by the cycle by the consumed energy L consumed by the compressor. Therefore, with the cycle configurations in Patent Documents 1 and 2, it can be expressed that the cycle efficiency is enhanced by reducing consumed energy L as compared with ordinary refrigeration cycle devices.
According to the above definition of cycle efficiency, the further enhancement of cycle efficiency can be expected by taking the following measure with the cycle configurations in Patent Documents 1 and 2: the refrigeration capacity ΔH delivered by the cycle, that is, the enthalpy difference (ΔH=Hout−Hih) between the enthalpy Hin of evaporator inlet-side refrigerant and the enthalpy Hout of evaporator outlet-side refrigerant is increased.
For example, in the economizer refrigeration cycle device disclosed in Patent Document 1, vapor-liquid two-phase refrigerant whose pressure is reduced to intermediate pressure is let to flow into a vapor liquid separator. The separated saturated vapor-phase refrigerant is drawn to the higher stage compression mechanism, and the separated saturated liquid-phase refrigerant is let to flow into the evaporator by way of a pressure reducing device. Therefore, the further enhancement of cycle efficiency may be expected by reducing the enthalpy of the saturated liquid-phase refrigerant flowing out from the vapor liquid separator toward the evaporator.
To reduce the enthalpy of saturated liquid-phase refrigerant, a configuration for reducing the pressure of refrigerant may be used. However, if the pressure of refrigerant in the vapor liquid separator is reduced, the pressure of saturated vapor-phase refrigerant flowing out from the vapor liquid separator toward the higher stage compression mechanism is also reduced. Therefore, the pressure difference between drawn refrigerant pressure and discharged refrigerant pressure in the higher stage compression mechanism is enlarged, and there is a possibility that the cycle efficiency is degraded on the contrary.
More specific description will be given. The vapor liquid separator of the economizer refrigeration cycle device in Patent Document 1 just separates refrigerant flowing thereinto into saturated vapor-phase refrigerant and saturated liquid-phase refrigerant and lets the separated refrigerants flow to the downstream side. Therefore, the enthalpy of refrigerant flowing into the evaporator can be reduced but the pressure of refrigerant simultaneously flowing into the higher stage compression mechanism cannot be appropriately adjusted.
In the ejector refrigeration cycle device disclosed in Patent Document 2, the flow of refrigerant is bifurcated at a bifurcating portion placed upstream of the ejector. One flow of refrigerant is let to flow into the nozzle portion of the ejector; and the other flow of refrigerant is let to flow into the evaporator by way of the pressure reducing device. Therefore, the further enhancement of cycle efficiency may be expected by reducing the enthalpy of refrigerant flowing out from the bifurcating portion toward the evaporator.
Boiling of refrigerant can be accelerated to enhance nozzle efficiency by letting vapor-liquid two-phase refrigerant or liquid-phase refrigerant with air bubbles mixed therein flow into the nozzle portion. Therefore, the enhancement of nozzle efficiency may be expected by letting vapor-liquid two-phase refrigerant higher in enthalpy than liquid-phase refrigerant flowing out from the bifurcating portion toward the nozzle portion. The nozzle efficiency refers to energy conversion efficiency obtained when the pressure energy of refrigerant is converted into kinetic energy at the nozzle portion.
However, the bifurcating portion of the ejector refrigeration cycle device in Patent Document 1 just has a function of producing a swirl flow in refrigerant flowing into the nozzle portion, in order to enhance nozzle efficiency. Therefore, refrigerant let to flow into the nozzle portion of the ejector may be brought into a vapor-liquid two-phase state but the enthalpy of refrigerant let to flow into the evaporator cannot be reduced.